1. Field of the Invention
The present invention generally relates to magnetic tape recording apparatuses and methods and magnetic tape formats, and to recording media therefor. More specifically, the invention relates to a magnetic tape recording apparatus and method for recording or reading high-quality video data on or from magnetic tape. The invention also relates to a magnetic tape format for use in the above-described magnetic tape recording apparatus and method and to a recording medium for storing a program implementing the above-described method.
2. Description of the Related Art
Along with advanced compression techniques, video data can be compressed and recorded on magnetic tape according to the digital video (DV) system. The format for use in the DV system is defined as a DV format of consumer digital video cassette recorders.
FIG. 1 illustrates the configuration of one track of a related DV format. In the DV format, video data is recorded after being subjected to 24-25 conversion. The numbers of bits shown in FIG. 1 represent numbers after 24-25 conversion has been performed on the video data.
The length of one track is substantially equal to a portion of magnetic tape up to a winding angle of 174 degrees. Outside the one-track portion, a 1250-bit overwrite margin is formed for preventing data from remaining recorded.
The length of one track is 134975 bits when a rotary head is rotated in synchronization with a frequency of 60×1000/1001 Hz, and is 134850 bits when the rotary head is rotated in synchronization with a frequency of 60 Hz.
In the one-track portion, an insert and track information (ITI) sector, an audio sector, a video sector, and a subcode sector are sequentially disposed in the tracing direction of the rotary head (from the left to right in FIG. 1). A gap G1 is formed between the ITI sector and the audio sector, a gap G2 is formed between the audio sector and the video sector, and a gap G3 is formed between the video sector and the subcode sector.
The length of the ITI sector is 3600 bits. In the ITI sector, a 1400-bit preamble for generating a clock, a start sync area (SSA), and a track information area (TIA) (1920 bits in total are assigned to the SSA and the TIA) are sequentially disposed. In the SSA, the bit string (sync number) required for detecting the position of the TIA is indicated. In the TIA, information indicating whether the format is a consumer DV format and whether the format is an SP mode or an LP mode, and information concerning the pattern of a one-frame pilot signal is recorded. After the TIA, a 280-bit postamble is disposed. The length of the gap G1 is 625 bits.
The length of the audio sector is 11550 bits. The first 400 bits and the last 500 bits serve as a preamble and a postamble, respectively, and the remaining 10650 bits between the preamble and the postamble is used as audio data. The length of the gap G2 is 700 bits.
The length of the video sector is 113225 bits. The first 400 bits and the last 925 bits serve as a preamble and a postamble, respectively, and the remaining 111900 bits between the preamble and the postamble are used as video data. The length of the gap G3 is 1550 bits.
The length of the subcode sector is 3725 bits when the rotary head is rotated at a frequency of 60×1000/1001 Hz, and is 3600 bits when the rotary head is rotated at a frequency of 60 Hz. The first 1200 bits and the last 1325 bits or 1200 bits (depending on the frequency of the rotary head as discussed above) serve as a preamble and a postamble, respectively, and the remaining 1200 bits between the preamble and the postamble are used as subcode data.
FIG. 2 illustrates the configuration of the video sector shown in FIG. 1. The video sector is formed of 149 90-byte sync blocks, as shown in FIG. 2. Among the 149 sync blocks, 138 sync blocks are formed of a two-byte sync, a three-byte ID, 77-byte video data, and parity C1 (inner error correcting code). In the remaining 11 sync blocks, 77-byte parity C2 (outer error correcting code) is substituted for the video data.
In the DV format, not only the provision of the gaps G1, G2, and G3, but also a preamble and a postamble are formed for each sector. That is, the so-called “overhead” is large, and a sufficient recording rate cannot be obtained for the real data.
About 25 Mbps are required for recording high-quality video data (hereinafter referred to as “high definition (HD) video data”). In the above-described recording format, however, only 24 Mbps are ensured for the data compressed by the main profile/high level (MP@HL) method in the MPEG system, except for search image data. As a result, although standard-quality video data (hereinafter referred to as the “standard definition (SD) video data”) can be recorded, HD video data cannot be recorded after being compressed with the MP@HL or MP@H-14 method.
Additionally, the MPEG method is becoming mainstream for compressing video data. The unit of transport stream (TS) packets of the MPEG-compressed video data is 188 bytes. To dispose such a transport packet in the synch blocks of the video sector shown in FIG. 2, three sync blocks are required, since each sync block is 77 bytes, (231 bytes (=77 bytes×three sync blocks)), thereby causing a redundancy of 43 bytes. Thus, each sync block has about 14 redundancy bytes.
In this manner, according to the DV format, transport packets cannot be efficiently recorded.